Synchronous servo-control



Lain.

1956 J. MERCIER 2,768,613

SYNCHRONOUS SERVO-CONTROL Filed Jan. 4, 1955 INVENTQR Lfean Merci e1 ATTORNEYS United States Patent SYNCHRUNOUS SERVG-CONTRQL Jean Mercier, New York, N Y.

Application January 4, 1955, Serial No. 479,838 Claims priority, application Belgium February 27, 1948 9 Claims. (Cl. 121-411) This specification is a continuation-in-part of my copending application No. 356,984, filed on April 6, 1953, now abandoned, divided out from my Patent No. 2,634,387 of 7th of April 1953.

The present invention relates to those servo-controls which enable any two phenomena to be synchronized and, in particular, the displacement of a driven or controlled member and of a reference member executing any movement. The driven and reference members will be hereafter collectively designated, whenever possible without ambiguity, by the expression the two members.

The servo-control according to the invention essentially comprises a source of energy, a motor fed from said source through a distributor of energy and adapted to impart the driven member with such an acceleration or deceleration, either alone or as an aid of other existing motor means, that said driven member may be rapidly reset into synchronism with the reference member, upon any acceleration or deceleration of the latter, and pilot means to control said distributor and, hence, the operation of said motor.

The main purpose of the invention is to design the said pilot means in such a manner that, upon any shift in position bet-ween the two members, they trigger the distributor to impart the driven member with the maximum possible acceleration or deceleration and then, after a time determined as a function of the shift position and difference of speeds between the two members they correct at each instant, again as a function of positional shift and speed difference, the said acceleration (or deceleration), in such a manner as to re-establish the said synchronism as quickly as possible without producing beats.

Provision is particularly made for servo-controls of the type described, in which no mechanical subjection in position is provided between the pilot means and the distributor.

It will be understood that this will obviate the necessity and even the utility, of the corrections that have hitherto been necessary with devices comprising a subordination of the pilot means to the distributor that enabled beats to be avoided, but had, on the contrary, the disadvantage of creating shifts as a function of the velocity of the system under consideration, the return shifting necessitating particular arrangements which are in this Way eliminated.

The invention has also for its purpose to provide a servo-control of the type described which is comparatively simple, while ensuring a safe operation.

In particular, to obtain an action as a function of the difference of speeds between the two members, it is advantageous to use hydraulic devices as pilot means, since this permits to control a displacement as a function of speed by merely flowing a liquid through a passage of appropriate cross-section.

With these purposes in view, the main object of the in- Vention is to provide a servo-control of the type described, wherein the distributor has a neutral position and two active positions in each of which it causes actuation at full rate of the motor in one of two directions and wherein the pilot means are essentially constituted by two intercommunicating hydraulic units adapted to control, as a function of the shift in position and difierence of speeds between the two members, triggering means adapted in turn to set said distributor selectively in either one of said three positions, for each value of the shift, according as whether the speed of the driven member is correct, insufficient or too great for ensuring rapid resetting without any beat.

Another object of the invention is to so design the above mentioned hydraulic units that the piston of the first one be displaceable with detecing means, the position of which is a function of the shift in position between the two members, while the piston of the second one is more or less displaced, during the resetting phase only, as a function of the difference of speeds between the two members, this last action being obtained by so designing the said intercommunicating hydraulic units that the piston of the first one exerts a thrust on that of the second during the said resetting phase, during a column of liquid and by providing the second hydraulic unit with a calibrated passage intercommunicating both sides of its piston and with a calibrated spring resisting the displacement of said piston under the action of said liquid column.

A further object of the invention is to provide a servocontrol of the type described wherein said triggering means are constituted by two electro-magnets system operatively connected with said distributor and adapted to be selectively energized, either separately or simultaneously, to selectively set said distributor in one of said three positions, said selective energizing being controlled by electric contacts selectively actuated according to the configuration of the pistons of said hydraulic units.

The invention will be better understood by the aid of the accompanying drawing, in which an embodiment has been given as an illustration only and not intended to define the scope of the invention.

In this drawing:

Fig. 1 is a diagrammatical sectional view of a synchronous servo-control according to the invention, and

Fig. 2 is a diagram showing curves of displacement of the standard of reference and of the driven member.

For simplification purposes, the motor fed through the servo-control according to the invention has been shown as a differential hydraulic unit or servo-motor 1, having a cylinder with a piston 5 slidable therein. Similarly, the reference member has been shown as a hand-lever 2 pivoted at 3 on the rod 4 of piston 5 of the said unit 1, the said control-lever 2 being furthermore pivotally connected through a connecting rod 6 to one end of an arm 62 pivoted at 8 on a fixed support 9. Finally, the driven member has been shown as a lever 2 pivoted at 3 on the rod 4 and having a connecting rod 6' articulated on a fixed support (not shown). In these conditions, the angular position of the arm 62 will indicate, at each instant, the relative position or phase relationship between the two members 2 and 2 to be synchronized, while an angular displacement of said arm 62 will take place if the speeds of said members are different, the speed of said angular displacement of the arm 62 being a function of the difference of the speeds between the members 2 and 2'. The annular compartment 7 of the hydraulic unit 1 is continuously fed through a pipe 10 from a pump 11. The cylindrical compartment 12 of the unit 1 communicates through a pipe 13 with a chamber 14 of a distributor 29 which, in the example illustrated, is of the type described in the U. S. application, Serial No. 2,286, filed January 14, 1948, for Hydraulic Follow-Up Systems, by Jean Mercier and Pierre Audemar. When the actuating member 15 of the said distributor is displaced towards the left (on the drawing) against the action of the spring 16, the said chamber 14 is set into communication with the pump 11 through a conduit communicating with the EtbOVE-H'KSBi ed pipe When the said actuating member 15 of the distributor 2? is displaced towards the right (always in the drawing), against the action of spring 17, the said chamber "14- is set into communication with an evacuation outlet 31. The actuating member 15 of the distributor 2% is rigid with a core member 5A) adapted to be moved toward the left or the right, res-occtively, when a solenoid '75 or a solenoid 7 respec is, is energized. Both solenoids '74 and 75 have one end commonly connected to one pole of a battery 76, the other pole of which is connected in parallel with two contacts 78 and 79, which will be further referred to, hereafter. The opposite ends of the solenoids 74, 75 are connec ed, respectively, with contacts 7T.-72, adapted to cooperate with the above mentioned contacts 73, 79 and both carried by a support 6? pivoted at 76 on a casing 13 containing the pilot means of the servo-control. The said pilot means are essentially constituted by two hydraulic units such as dashpots 55 and 56, controlling respectively the above mentioned contacts 71-73, '72 79. The hydraulic unit 55 has a piston 59 provided with two rods 63 and 2d. The rod 2% bears on the left side of the arm 62, which is continuously subjected on its right side, to the action of a spring 6t). The other rod 63 of the piston 59 carries the above mentioned contact 73.

Two passages 82 and 83 connect the compartments of the unit 55 under the control of valves 84 and 35, respectively.

When the piston 59 is located on the left of its midposition shown in Fig. l, the valve 84 is continuously urged into closed position by a plate P-ll, separate and distinct from the valve 8 and against which a spring 36 reacts, while an abutment or stop 21 in the path of said plate P-l prevents said spring from acting upon said valve 84 when the piston 59 is located on the right of the said mid-position.

Similarly, a spring 37 reacting against a plate P-2, separate and distinct from valve 8-5 urges said valve 35 into the closed position, while the piston is located on the right of said mid-position while an abutment or stop in the path of said plate P2 prevents said spring from acting, when the piston is located on the left of said midposition. The left-hand compartments of both units 55, 56 are connected through a duct 57, while another duct 53 also connects their righthand compartments.

The piston 64 of the second unit 56 is provided with a restricted passage 31.

The piston 64 also carries two rods, respectively 68 and 23, the first one of which carries the above-mentioned contact 79, while the other one, 25, is terminated at its right end by a head 23 freely slidable on a fixed support 24 and bearing at rest on a plate 66 against which presses a spring 65. The action of the said spring urges the piston 64 towards the left, limited at the mid-position of the piston 64, as shown in Fig. l, by the abutment of plate 65 against the support 24. Similarly, another spring 67 urges the piston 64 toward the right, the action of said spring being limited, at the mid-position of said piston by the abutment of a plate 66 against the fixed support 24. The pivoted arm as carrying the contacts 71 and '72 is urged counterclockwise (as shown in Fig. l) by a spring 73. Finally, a spring 61, the strength of which is negligible, as compared with that of the springs 61?, 6'7, 65 and 73, continuously urges the piston .59 towards the right.

In the example shown, the action of the spring 73 on the pistons 59 and 64 is assumed to be twice the action of the spring 6d, on the piston 59 as well as that of the spring 67 on the piston 64 while the strength of the spring 65 is assumed to be three times higher than the strength ofeach of the springs at) and 67. With this arrangement, it 15 easy to find that, at rest, each piston will be resiliently held in neutral position on a fixed abutment, while, when taken away from its neutral position in either direction, each piston will be continuously urged towards the said neutral position by a resilient action equal to that of each of the springs 6l67.

This device operates as follows:

Again, for simplification purposes, both members 2 and 2 will be first assumed to be at rest, with a relative position arbitrarily chosen to represent positional agreement, since it is obvious that the device would operate exactly in the same manner if said members were both moving with synchronized speeds and positions.

It will be then assumed that the reference member 2 is suddently displaced and then held stationary at a new position. The device would operate in the same manner if the reference member were given a sudden acceleration (or deceleration) and then held at a constant speed.

Finally, the driven member will be assumed to be brought by the servo-control to a new stationary position agreeing with the new position of the reference member. The servo-control would operate in the same manner to reset the driven member into synchronism of speed and position with the reference member.

At rest, the arm 62 is in the neutral position shown in Fig. l, in which both pistons 59 and 64 are in their midposition, thus establishing both contacts 7173 and 7279. Both solenoids 74- 75 are energized, thus urging the core member 89 with equal and opposite forces. As a result, said core remains stationary in its neutral position, in which the distributor 29 interrupts communication of the cylindrical compartment 12 of the hydraulic unit 1, both with the pump 11 and the outlet 31.

it will be now assumed that the control lever 2 has been suddenly displaced clockwise. As soon as this displacement begins, the speed of member 2 becomes higher than that of member 2'. in these conditions, the arm 62 is angularly displaced counterclockwise against the compression of the spring 6%, so that the spring 61 urges the piston towards the right. Since the spring 36 is made inoperative by reason of the abutment of plate P-l against stop 21, the liquid in the right compartment of the piston 59 may flow freely through the passage 32, by moving the valve 84, toward the left-hand compartment of the unit 55. The piston 6- 5 thus remains stationary in its mid position and its spring holds the contact-carrying arm 69 against the action of the spring 73. Thus, the contacts 7i78 are separated, so that only the solenoid remains energized. The core member 853 is attracted towards the left and the distributor 29 sets the compartment 12 of the hydraulic unit 1 into communication with the pump 11. Both compartments of the hydraulic unit 1 being fed at the same pressure, the piston 5 is urged towards the right with a constant force. In other words, the driven member 2' is accelerated.

When the reference member 2 becomes stationary in its new position, the speed of the driven member 2 becomes at once higher than that of the said reference member, the speed of which is nil. The arm 62 then begins to move in a clockwise direction in view of its connection to means and 6 thus moving the piston 59 to the left towards its rnidposition. As the valve 84 is separated from plate P-Z, the valve 84 will close to prevent liquid flow through passage 82, While the valve 85 seated under the action of the spring 87 against plate P-2 also prevents liquid from flowing through the passage 83. in these conditions, the displacement towards the left of the piston 59 sends liquid from the left-hand compartment of the unit 55 into the left-hand compartment of the unit 55, through pipe 57. This liquid tries to pass from the left to the right through the passage 81,

while the piston 54 resists any displacement towards the right with a resilient force equal to the difference of strengths between the springs 65 and 73, i. e. equal to the strength of spring 67 (which is then inoperative due to the abutment 6624).

In these conditions, piston 64 is more or less displaced towards the right asan increasing function of the speed of displacement of the arm d2 i. e. of the difference of speeds between the two members 2-2. Both contacts 71 and 78 are thus moved towards each other and during the return stroke of the piston 59, i. e. While the speed of the driven member has become higher than that of the reference member, at a point which is the closer to the neutral position of the piston 59 (corresponding to positional agreement between the two members) as the speed of the driven member is nearer the ideal value for the purposes aimed at.

As a result of the above described process of operation, it may be seen that the controlled member is continuously accelerated, in response to the assumed shift, until its speed becomes so high, for the value of the remaining shift, that it would risk to overreach the new position of the reference member 2. Then contacts 7l-78 being re-established as described above, the controlled member 2 is no more accelerated.

Now, piston 5? continues to move towards its neutral position, under the action of spring 60 and the positive action of arm 62, while piston 64 is urged towards the left by its spring 65 and towards the right by the liquid forced through line 57 by piston 58. In these conditions, if the speed of the arm 62 is too great for the purposes aimed at, the piston 54 will not follow the contact arm 69 (said piston being either displaced slower or held stationary of even displaced in the opposite direction, i. e. towards the right), contact 7279 will be interrupted alone, the compartment 12 of hydraulic unit 1 will be set into communication with the outlet 31 and the controlled member will be braked.

Conversely, if the said speed is too small, the piston 64 will move towards the left quicker than the piston 59, the contact 71- 78 will be re-interrupted alone and the driven member will be accelerated anew. Finally, if the speed is correct, both contacts will remain established and the driven member will be left to itself.

With this arrangement, it is clear that, if the passage and the springs are suitably calibrated, the speed of the controlled member will be first increased with the maximum possible acceleration, until the instant at which both contacts are first re-established and then suitably corrected until the arm 6?. has reassumed its neutral position so that positional agreement between members 2 and 2' will be re-established in the minimum possible time and substantially without any beat.

The device operates in the same manner when the arm 62 is first displaced clockwise, except for the behaviour of the springs which is obtained by different but equivalent combinations.

Fig. 2 shows the more general operation of the system in the case when both reference and driven members are moving at different speeds.

Referring to Fig. 2, the broken line a, d, e, at shows the motion of the standard of reference, and the curve b, c, b2, d, e, [73, b4, 1, be, the motion of the driven member. This motion is here expressed as the variation of an angle plotted against time. Assuming that the standard of reference has taken up a certain speed, and that the driven member is accelerated to enable it to overtake the standard of reference, it will be understood that the driven member will move along a curve of parabolic form. When the driven member arrives at the point b, at which its speed is equal to that of the standard of reference, the action due to the difference in speed is completed. When the driven member reaches the point c, that is to say, when its speed has exceeded by a certain value the speed of the standard of reference, the device according to the invention intervenes to diminish its speed, in such a way that instead of following the branch b1 of the curve it will follow the line b2, which will tend to become tangential to the line a, the angle a between the tangent to the curve b and the straight line a, represent- 6 ing the difference between the speeds, tending progres sively to diminish. Starting from the point d, at which the curve b2, has become merged in the straight line a, the two members move without relative angular displacement.

It will now be assumed that at the point e, the standard of reference has undergone a retardation. From this point onwards, it will then follow the straight portion a1, while the driven member will continue to move along the straight portion be. At this juncture, a retardation is applied to the driven member and it will consequently follow a curve b4 of parabolic form. When it reaches the point 1, its speed having become lower than the speed of the standard of reference, an acceleration will again be imparted to it, so that instead of following the branch be, it will follow the curve be, the angle a between the straight portion at and the tangent to the curve b4 diminishing progressively until the two trajectories merge into one.

It will be understood that the invention is in no way restricted to the forms of construction described and illustrated, and that it may be embodied in many other forms that will be obvious to those skilled in the art, without going outside its ambit, or departing from its spirit.

What I claim is:

l. A servo-control for controlling the position of a driven member in dependence upon the position of a reference member, comprising motor means to drive said driven member in two opposite directions, distributor means having a neutral position and two operative positions to control operation of said motor means, movable detecting means associated with said members to be moved thereby, in response to variations of their position, at a speed which is a function of their relative speed, a first hydraulic dashpot unit having a piston displaceable in unison with said detecting means, a second hydraulic dashpot unit having a piston, and resilient means reacting against said piston, the latter being displaceable against the action of said resilient means in response to liquid pressure caused by a displacement of said first piston when said detecting means is moved in accordance with a decrease of positional disagreement between said members, said second piston having a restricted passageway therethrough to provide communication between the cylinder spaces on both sides of said second piston, whereby the displacement of said second piston is a function of said detecting means speed, and triggering means interposed between said pistons and distributor means to selectively set the same into one of the said three positions according to the positions of the said pistons.

2. A servo-control according to claim 1, in which said triggering means comprise two electro-magnets operatively associated with the said distributor means to set the same into its neutral position when they are both simultaneously energized and into one of said operative positions, when only one of them is energized, and two electric contacts, each interposed in the energizing circuit of one of said electro-magnets and adapted to be actuated by said pistons selectively to complete one or both of said energizing circuits, according to the positions of said pistons.

3. A servo-control according to claim 1, wherein said detecting means comprises a pivoted arm differentially actuated from said two members, means being provided to make the piston of said first unit positively displaceable with said pivoted arm.

4. A servo-control according to claim 3, wherein said last named means comprises a rod rigid with said first piston, spring means continuosuly to urge said rod into bearing contact with said pivoted arm and spring means continuously to urge said pivoted arm into bearing contact with said rod.

5. A servo-control according to claim 1, wherein the cylinders of said first and second hydraulic units are connected on either sides of said pistons, passage means are provided to connect the cylinder spaces on either side of said first piston, said first piston is displaceable in response to motion of said detecting means on either side of a neutral position, and valve means are provided to permit flow of liquid through said passage means when said piston is moved from said neutral position, while preventing liquid from flowing through said passage means when said piston is displaced towards said neutral position.

6. A servo-control according to claim 1, wherein said detecting means and pistons are each displaceable on either side of a neutral position, the neutral position of said detecting means being in accordance with that of first piston, and wherein spring means are provided continuously to urge said detecting means and pistons towards their neutral position upon any shift therefrom.

7. A servo-control according to claim 2, wherein each one of said electric contacts comprises two elements, one ofwhich is rigid with one of said pistons, the two remain ing elements of said contacts being mounted on a common pivoted support, spring means are provided continuously to urge said pivoted support into contact-making position with said contact elements solid with said pistons, each one of said pistons is displaceable on either side of a neutral position, and spring means are provided continuously to urge each one of said pistons towards said neutral position upon any shift therefrom, the relative calibrations and the arrangement of said spring means, as well as the relative arrangement of said contact elements being such that, at each position of said first piston, both of said contacts are simultaneously established only for a well-defined position of said second piston, this being the case, in particular, when both pistons are in neutral position, while for any other position of said second piston, only one of said contacts is established.

8. A servo-control according to claim 1, wherein said motor means is of liquid pressure type, and wherein said distributor means is constituted by a three-position hydraulic distributor.

9. A servo-control according to claim 8, wherein said distributor is of the type ensuring full rate flow of liquid towards or away from said motor means upon the slightest shift of said distributor from its neutral position.

References Cited in the file of this patent UNITED STATES PATENTS 1,472,885 Perham Nov. 6, 1923 1,887,335 Sperry Nov. 8, 1932 2,588,522 Harris Mar. 11, 1952 

